The present invention relates to a method of measuring the reflectivity or absorbency of an item to electromagnetic radiation and to a reflectometer for performing said method. Without limitation, the invention also relates to a method of determining the dielectric properties, for example relative permittivity, of said item and to a measurement apparatus for performing said method. Such a method and apparatus are suitable for non-destructive, quality assurance assessments of items during manufacture. Without limitation, the present method and apparatus find application in the characterisation of the radio-frequency (RF) properties of wind turbine blades.
Radar absorbing materials (RAMs) are employed in composite aerofoil structures such as aircraft wings and wind turbine blades in order to reduce the radar cross-section (RCS) of said structures. This is particularly important for new wind farms in order to reduce undesirable effects of the wind turbine blades on air-traffic control (ATC) radar and air-defence radar (ADR).